Hybrid network nonisocyanate polyurethane materials are completely different, in structure and in properties, from linear and network polyurethanes produced from oligomers and/or starting materials comprising isocyanate groups.
The conventional method of producing linear and network polyurethane compounds is based on the reaction between oligomers with terminal hydroxyl groups and oligomers with terminal isocyanate groups. This method is disadvantageous because it uses toxic isocyanates, which are produced from an even more dangerous component, phosgene. Another principal limitation of the conventional polyurethane method of production is the more highly porous material which it yields. Because the conventional urethane-forming reaction is sensitive to moisture, an undesirable side-reaction with water leads to the formation of carbon dioxide gas within the polyurethane during its production. These gas bubbles give rise to the increased porosity of such polyurethane products.
Moreover, conventional polyurethanes derived from isocyanates are not suitable for use in many applications, e.g., as composite matrix materials, mastics, etc., because they have an inherent weakness arising from their molecular composition. Within their polymer structure are hydrolytically unstable chemical bonds which make these materials highly vulnerable to environmental degradation. For example, the use of conventionally produced polyurethane matrix materials is limited by their hydrolytic instability and their poor chemical resistance to aqueous solutions of acids and alkalies.
By modifying the structure of the polymer, a promising method of raising mechanical performance and hydrolytic stability is introduced in the form of a nonisocyanate polyurethane network, a modified polyurethane with lower permeability and increased chemical resistance properties to aqueous solutions of acids and alkalies. Moreover, nonisocyanate polyurethane networks are made by a synthesis process that uses far more environmentally benign materials than isocyanates and phosgene.
The preparation and properties of linear nonisocyanate polyurethanes is disclosed by W. J. Blank ["Non-Isocyanate Routes to Polyurethanes", Proceedings of the 17th Water-Borne and Higher Solids Coatings Symposium, New Orleans, La., Feb. 21-23, 1990, pp. 279-291]. The preparation of a dihydroxy terminated nonisocyanate polyurethane diol, its self-condensation, and the condensation of this diol with other diols, such as polytetramethylene glycol and hydroxy terminated polyester, is disclosed. However, this publication does not teach that nonisocyanate polyurethane networks may be formed, that a reactant comprising terminal cyclocarbonate groups may be used to form a nonisocyanate polyurethane network, or that a reactant comprising terminal primary amine groups may be used to form a nonisocyanate polyurethane network.
Additionally, U.S. Pat. No. 5,340,889 to Crawford et al. discloses a method for producing linear nonisocyanate polyurethanes based on the reaction between the oligomeric bifunctional cyclocarbonate oligomers described therein and amines. However, polyurethanes formed by this method, because they lack a cross-linked network structure, cannot be used for construction and structural materials. Moreover, for the same reason, these materials are not very chemically resistant to aqueous solutions of acids and alkalies.
The above-described deficiencies in conventional linear polyurethanes, conventional network polyurethanes and linear nonisocyanate polyurethanes can be remedied by the formation of a network comprising nonisocyanate polyurethanes. For example, after hardening by cross-linking or curing, network nonisocyanate polyurethanes may be used as the matrix of composite materials which serve as structural components. Moreover, these materials are also useful as:
nonporous monolithic coatings, coverings and linings, which can be used for the corrosion protection and wear protection of concrete, metallic and wood surfaces; PA1 hydrolysis-stable and gasoline-stable sealants, which can be used for protection of electronic devices and their components, in aircraft and rocket construction and, mainly, for civil engineering applications; PA1 glues with high adhesion strength and longevity, which can be used for joining all types of materials, e.g., metals, ceramics, glass, etc.; PA1 reinforced and highly-filled polymers, which can be used for civil and chemical engineering applications. PA1 (a) selecting least one oligomer terminated with a plurality of cyclocarbonate groups, the cyclocarbonate-terminated oligomer further comprising from about 4% to about 12% by weight of terminal epoxy groups based on the weight of terminal cyclocarbonate groups present, where the oligomer has an average functionality towards primary amines of from about 2.0 to about 5.44; PA1 (b) selecting at least one other oligomer terminated with a plurality of primary amine groups, where the amine oligomer has an average functionality towards cyclocarbonate groups of from about 3.0 to about 3.8; PA1 (c) mixing the oligomers in an amount to form a mixture with a pot life such that the amount of the amine oligomer(s) present is from about 0.93 to about 0.99 of the amount of the amine oligomer(s) that would be required to achieve a stoichiometric ratio between the primary amine groups of the amine oligomer(s) and the cyclocarbonate groups of the cyclocarbonate-terminated oligomer(s); and PA1 (d) curing the mixture at a temperature of from about 10.degree. C. to about 140.degree. C. to form a hybrid nonisocyanate polyurethane network polymer with a gel fraction of not less than about 0.96 by weight.
Other potential areas where nonisocyanate polyurethane networks are useful include automotive applications, such as for bumpers, dashboards, seating, trim components, truck beds and repair putty; construction applications, such as concrete additives, flooring and crack barriers; marine applications, such as decking; and consumer products, such as appliances, footwear, furniture and toys.
Nonisocyanate polyurethane matrices which are intended for applications such as those described above must be characterized by a relatively high level of mechanical properties, such as high tensile strength and high relative elongation, and also have low porosity, high hydrolytic stability and high chemical resistance to aqueous solutions of acids and alkalies. Also, the process of making these compounds is desirable because it uses nontoxic reactants.
U.S. Pat. No. 1,754,748 discloses an epoxy resin-based composite material used for monolithic flooring. The compositions of this reference also contain an oligomeric dicyclocarbonate modifier and, as a hardener, an aminophenol which is monofunctional toward the cyclocarbonate terminal groups of the modifier. Thus, these materials do not comprise a nonisocyanate polyurethane network but comprise, as a matrix, an epoxy polymer network which immobilizes a small amount of linear, low-molecular weight nonisocyanate polyurethane formed from the oligomeric dicyclocarbonate and aminophenol.
U.S. Pat. No. 5,175,231 to Rappoport et al. discloses the formation, in a multi-step process, of a network comprising nonisocyanate polyurethane links in its structure. The disclosed network is formed from reactions in which a cyclocarbonate is reacted with an amine and an amine is reacted with an epoxide, however, the reactants used and the method of network formation are completely different from the present invention. This patent discloses that, in a first step, oligomers comprising cyclocarbonate are formed from epoxide resins. Then, an end-capping step is carried out in which these oligomers are end-capped with a diamine, the two amine groups of the diamine reactant having different reactivity. Finally, the amine end-capped oligomer is cross-linked by reacting it with an epoxy resin to form a network structure. In contrast, the present invention differs, inter alia, by not requiring diamines where the two amine groups of the diamine have different reactivity, nor does it require that epoxy resins be used to provide cross-linking.